CN107429567B

CN107429567B - Turbine, organic rankine cycle or kalina cycle or steam cycle apparatus

Info

Publication number: CN107429567B
Application number: CN201680016506.9A
Authority: CN
Inventors: R·比尼; M·盖亚; D·科伦坡
Original assignee: Turboden SpA
Current assignee: Turboden SpA
Priority date: 2015-04-03
Filing date: 2016-03-21
Publication date: 2021-03-23
Anticipated expiration: 2036-03-21
Also published as: CA2975968C; EP3277929B1; WO2016157020A3; ES2959679T3; US10526892B2; BR112017021062B1; CN107429567A; PL3277929T3; JP6657250B2; CA2975968A1; JP2018513299A; RU2716932C2; BR112017021062A2; RU2017131761A3; HRP20231218T1; US20180283177A1; RU2017131761A; EP3277929A2; WO2016157020A2

Abstract

The invention relates to a turbine of an Organic Rankine Cycle (ORC). The turbine includes a shaft supported by at least two bearings and a plurality of axial expansion stages defined by an array of stator blades alternating with an array of rotor blades. The rotor blades are supported by corresponding bearing disks. The main support disc is directly coupled to the shaft in an external position with respect to the bearings, and the remaining support discs are constrained one after the other on the main support disc, and not directly on said shaft. The proposed solution allows to obtain a cantilevered configuration of the turbine while still having a plurality of stages. Some of the remaining support disks are constrained to the main support disk and extend in a cantilevered fashion from the same side of the bearing that supports the shaft, so that the center of gravity of the rotor portion of the turbine is shifted more toward the bearing.

Description

Turbine, organic rankine cycle or kalina cycle or steam cycle apparatus

Technical Field

The invention relates to a turbine designed for operating preferably under an Organic Rankine Cycle (ORC) or kalina cycle or a steam cycle.

Background

The acronym ORC "organic rankine cycle" generally denotes a rankine type of thermodynamic cycle that uses an organic working fluid, usually with a higher molecular mass than water vapor, which is used by most rankine power cycles.

ORC plants are commonly used for the combined production of electrical and thermal energy from solid biomass; other applications include the extraction of waste heat from industrial processes, the recovery of heat from prime movers or geothermal or solar sources.

For example, ORC plants fed with biomass typically include:

-a combustion chamber fed with biomass fuel;

-a heat exchanger arranged to transfer a portion of the combustion fumes/gases to a heat transfer fluid, such as diathermic oil, conveyed through an intermediate circuit;

-one or more heat exchangers arranged to transfer a portion of the intermediate heat transfer fluid to the working fluid, thereby causing its preheating and evaporation;

-a turbine powered by a working fluid in a vapour state; and

a generator driven by the turbine to produce electricity.

In the heat exchanger downstream of the combustion chamber, a heat transfer fluid, such as diathermic oil, is heated to a temperature of typically about 300 ℃. The heat transfer fluid circulates in a closed loop circuit so as to flow through the heat exchanger in which the organic working fluid is evaporated. The organic fluid vapour expands in the turbine, thereby generating mechanical power which is then converted into electric power via a generator connected to the shaft of the turbine itself. As the working fluid vapour finishes its expansion in the turbine, it condenses in a specific condenser by transferring heat to a cooling fluid, usually water, which is used downstream of the plant as a heat carrier at about 80-90 ℃, for example for central heating. The condensed working fluid is fed into a heat exchanger in which the heat transfer fluid flows, thereby completing a closed loop cycle. Typically, there is also a regenerator that cools the vapor at the turbine output (before the condenser input) and preheats the organic liquid upstream of the preheater/evaporator.

The generated power may be used to operate auxiliary devices of the apparatus and/or may be directed into a power distribution network.

In ORC plants characterized by high expansion ratios and high enthalpy changes of the working fluid in the turbine, the turbine should advantageously be provided with three or more stages, wherein a "stage" designates an array of sub-blades and a corresponding array of rotor blades.

As the number of turbine stages increases, so does the cost and project engineering and assembly become more and more complex, up to the limit where two turbines connected in series can be advantageously used to operate a single generator. Thus, instead of increasing the number of stages of a single turbine, for example up to six stages or more, two turbines each having three stages may be employed.

For example, in an apparatus designed by the applicant for the production of 5MW, instead of using a single six-stage axial turbine designed for 3000 rpm, it has been chosen to use two axial turbines-one high pressure turbine and one low pressure turbine-connected to a single generator on opposite sides of the latter by respective shafts.

Solutions using multiple turbines such as those described above involve several technical and economic drawbacks. The plant must be provided with several reduction units for coupling the turbine with the generator (except in case the turbine is dimensioned to allow a direct coupling solution without the need of a reduction unit), valves more for steam inflow in the low pressure turbine with respect to the high pressure inlet valve, double bearings and rotary seals, double housings, double shafts, double meters, insulated pipes fluidly connecting the turbines, etc. This causes an increase in the cost of manufacturing, adjusting and maintaining the equipment, as well as technical difficulties in calibrating, starting, stopping and operating the equipment.

The applicant has proposed a compromise between the use of two turbines and the manufacture of a single multi-stage turbine. Patent application WO 2013/108099 describes a turbine specifically designed to operate in an ORC cycle and comprising a centrifugal radial stage followed by a shaft flow stage. In one embodiment described, the turbine has a cantilevered configuration, i.e. the shaft is supported by bearings arranged on the same side with respect to the supporting disk of the rotor blade.

US 2,145,886 describes a radial turbine having a single support disk or two support disks, the latter being mounted in a cantilevered manner. A first disk (14 in fig. 1) supports a plurality of stages in the bi-directional rotating portion of the turbine; a second support disk (18) is coupled with the first disk and supports a plurality of stages in a unidirectional rotating portion of the turbine.

US 2,747,367 describes a gas turbine provided with a multistage axial compressor and a turbine. The shaft is not supported in a cantilevered fashion. The support disks or the low-pressure and high-pressure compressors and the turbine are screwed to one another.

For example, referring to fig. 3, a low pressure compressor is indicated by reference numeral 91. The shaft 88 is supported by three bearings 30, 128, 140 (fig. 3 and 5). There are two couplers 101 and 102 (fig. 3) and they are depicted (column 3, row 46) as outwardly extending flanges 101 and 102; rotor disks 92 are separated by the flanges.

Referring to fig. 4, a high pressure compressor is indicated by reference numeral 152. The shaft 182 is supported by three bearings 168, 170, 180 (fig. 3 and 4). There are two couplings 160 and 162 and they are described (column 4, row 52) as supports (endbells) for bearings 160 and 162; the rotor disk 154 (fig. 4) is separate from the support of the bearing.

Referring to fig. 5, the high pressure turbine 68 includes a single support disk constrained to a shaft 182 of the high pressure compressor, which shaft 182 is in turn supported by three bearings 168, 170 and 180 (fig. 3 and 4).

Referring to FIG. 5, low pressure turbine 74 includes two rotor disks; one rotor disk is constrained to the shaft 88 driving the low pressure compressor and the other rotor disk is constrained to the shaft 140. The two disks are also connected to each other so that the entire assembly is supported by the three bearings 30, 128 and 140 (fig. 3 and 5).

GB 310037 describes a counter-rotating radial turbine provided with two further axial stages per radial turbine. The two rotors are mounted in a cantilever fashion. As described on page 2, line 8, the turbine disk consists of

parts

3, 4 and 5 shown in fig. 1. The

radial stages

8 and 9 are mounted on the

parts

3 and 4, respectively, and do not cause a change in the position of the centre of gravity of the system in case of symmetry with respect to each other. The axial stages 10 and 11 (two to the left and two to the right) are necessarily mounted symmetrically with respect to the centre line of the machine (page 1, line 87 and below: "in fig. 1, a-a denotes a plane at right angles to the geometric rotation axis 1 of the turbine, around which plane the turbine is symmetrical"). Furthermore, the disks do not extend annularly in order to be able to accommodate the stator in the gap between two adjacent disks.

US 2,430,183 describes a bi-directional rotating radial turbine comprising counter-rotating reaction turbines (

disks

5 and 6 of fig. 1) and counter-rotating impulse turbines (disks 6 and 10). The outermost disc 10, which in fact does not have a disc shape, causes a displacement of the centre of gravity away from the bearings of the

shafts

3 and 4, thereby causing an increase in the moment.

Disclosure of Invention

One object of the present invention is to provide a turbine for a rankine ORC cycle provided with a supporting disc of rotor stages arranged in cantilever fashion with respect to the bearings of the shaft, which can be provided with a plurality of stages, even more than three, and which is easy to assemble anyway.

The first aspect of the invention therefore relates to a turbomachine described hereinafter, designed for an organic rankine ORC cycle or, secondarily, for a kalina cycle or a steam cycle.

In particular, the turbine comprises a shaft supported by at least two bearings and a plurality of axial expansion stages defined by an array of stator blades alternating with an array of rotor blades.

The rotor blades are supported by corresponding bearing disks.

Unlike conventional solutions, one of the support discs, hereinafter called main support disc, is directly coupled to the shaft in an outboard position with respect to the bearings, i.e. in a non-intermediate zone between the bearings, and the remaining support discs are constrained one after the other on the main support disc, but not directly on the shaft. In other words, preferably only the main support disc extends towards the turbine axis until it contacts the shaft.

The proposed solution allows to maintain a cantilevered configuration of the turbine, wherein the array of rotor blades is in fact supported by the shaft, although in the outer region with respect to the bearing, so that it is still possible to have a plurality of stages, even more than three if desired. Thus, the turbine may be designed to expand the working fluid at a high enthalpy change (similar to that which can be achieved by a conventional multi-stage axial turbine that is not cantilevered or by two coupled axial turbines with otherwise unchanged conditions).

As will be described in detail later, the cantilevered configuration according to the invention allows assembling and disassembling the turbine in a rather simple manner both in the building process and in maintenance. In short, the supporting disks of the rotor blades may be constrained to each other, simultaneously or in groups, to then be inserted "in stacks" in the volute, before also inserting the shaft and the respective disks.

Advantageously, at least some, if not all, of the remaining support discs are constrained to the main support disc and extend in a cantilevered manner on the same side of the bearing that supports the shaft. This allows shifting the centre of gravity of the rotating part of the turbine towards the bearing supporting it. As the number of support discs mounted in a cantilevered manner on the main disc increases, the center of gravity is correspondingly displaced towards the bearing system of the support shaft.

For example, US 2,145,886 describes a radial rather than axial turbine in which the additional stages do not shift the centre of gravity of the turbine at the axial position of the first stage, i.e. towards the bearing. Furthermore, the second disc, indicated by reference numeral 18, is mainly the second outermost part of the disc 14 that does not contribute to the formation of sufficient space for the stator between two consecutive discs.

US 2,747,367 describes neither a solution in which the main supporting disc and the other discs constrained thereto are provided, nor a "cantilevered" assembly solution.

Optionally, other support discs are constrained to the main support disc and extend in cantilever fashion from opposite sides of the bearing supporting the shaft. Obviously, as the number of these supporting disks increases, the center of gravity of the rotating part of the turbine tends to shift away from the bearing.

Preferably, all the support discs except the main support disc are provided with a large central hole, i.e. they extend annularly around the central hole; the central bore has a diameter greater than the outer diameter of the shaft such that an expanded volume is defined between each ring and the shaft. This volume or clearance may be used to house the stator portion of the bearing of the seal and the bearing (thereby allowing the turbine side bearing to be housed close to the rotor centre of gravity) and to insert the shaft through the disk which has been previously assembled on the volute, and for maintenance, to allow insertion of instruments, for example inspection instruments.

Preferably, the support discs are bolted to each other and the main support disc is constrained on the shaft by means of a coupling selected from: flanges provided with bolts or studs, Hirth teeth, conical couplings, cylindrical couplings with a splined or keyed profile. Preferably, as mentioned above, during the assembly step, the shaft may be inserted through the support disc/ring, which in turn has been inserted into the turbine volute; the bearing is later installed to complete the assembly.

In the preferred embodiment, the array of rotor blades located furthest from the main support disc on the bearing side is the high pressure rotor blade, i.e. where the working fluid expansion starts.

In the preferred embodiment, the turbine includes at least three support disks upstream of the main support disk, and sometimes one or more disks downstream of the main support disk and corresponding expansion stages of the working fluid.

In another embodiment of the turbomachine, the first stage of expansion of the working fluid is a radial stage of the centripetal or centrifugal type, depending on whether the working fluid expands by moving towards or away from the axis of the turbomachine, respectively. In this condition, the working fluid is diverted to expand in an axial stage disposed downstream of the first stage. This shunting takes place at so-called corner blades.

In the preferred embodiment, the turbine includes a stator portion, such as a spray volute of working fluid. The array of rotor blades is constrained to stator portions that alternate with the array of stator blades. To facilitate turbine assembly, the stator portion defines a stepped internal volume, wherein the steps are cut to form an increasing diameter in the expansion direction of the working fluid. The steps of the stator portion provide effective abutment and bearing surfaces for the array of stator vanes that can be easily secured thereto, even one by one.

Preferably, each support disc comprises at least one flanged portion projecting in cantilever fashion towards the flanged portion of an adjacent support disc for abutting coupling. The joined flanges of two adjacent support disks, together with the volute, define a volume in which the turbine blade assembly is confined and in which the working fluid expands. Preferably, one or more through holes are formed through the flanged portion of the disc to drain any liquid, such as a working fluid or a lubricating oil, in the liquid phase. In order to limit the leakage of pressurized working fluid during normal operation, in a constructive variant, a shut-off valve may be installed in each of these holes, the valve being configured:

closing the respective holes when the turbine is running, i.e. when the shaft is rotating, thereby preventing the passage of vapours of the working fluid therethrough,

opening the hole when the rotation speed of the turbine decreases (at the start or stop thereof) to allow any liquid fluid accumulated in the volume between the flange and the turbine shaft to drain (condensed working fluid or lubricating oil leaking from the mechanical rotary seal, or even water if present).

Obviously, for each disc, more valves arranged circumferentially on the flanged portion may be provided in order to maintain the balance of the disc during rotation.

Preferably, each valve comprises:

blocking members, such as metal balls, which can be inserted in corresponding through holes obtained in the flange of the supporting disk, and

a biasing elastic member, such as a spring, designed to constantly push the closing member in the position of the aperture. The pretension of the elastic element is such that the centrifugal force exerted on the closing element when the rotor reaches a given speed is higher than the pretension of the elastic element, so that the bore remains closed when the turbine is running and opens when the turbine is running at low speed or is completely stopped.

As an alternative, each valve comprises a spherical obturator and a respective housing, preferably held together by screws and provided with a set of blades of the internal cavity. The housing is partially open towards the aperture to be intercepted, so that at least a portion of the obturating member can project from its own housing towards the aperture. The elastic support member supports the housing in a cantilever manner; for example, the housing is constrained to the elastic support member, for example an elastic sheet fastened in turn to the support disc in the vicinity of the hole. After the bending of the elastic member, the blocking member intercepts the hole thereby closing it, or the blocking member moves away from the hole so that the latter remains open.

The applicant is prepared to submit a divisional application relating to a shut-off valve similar to the one described above, which can be used on a support disk in other types of turbines.

Preferably, one or more passages are obtained through the main support disc to discharge the working fluid. These holes allow the passage of the working fluid leaking from the labyrinth seals installed between the rotor blades and the stator blades, thus equalizing the pressure upstream and downstream of the disk itself.

In one embodiment, at least the first turbine stage, i.e. the first stage through which the fluid passes in the direction of expansion thereof, is of centripetal or centrifugal radial type. Especially in the case where the radial portion comprises more than one stage, this solution has an even greater number of stages, the axial dimensions of the turbines being equal.

Furthermore, the use of one or more radial-type centripetal or centrifugal stator arrays provides the advantage of facilitating the use of variable-pitch stators in the foremost arrays, since the individual blades can rotate about axes that are parallel to each other (and to the shaft) and not otherwise oriented (as in axial arrays). The mounting of the stator that can be oriented and operated as a valve may be sufficient to provide this function without requiring an actual full stage.

Preferably, the turbine comprises a volute and the head of the shaft has a diameter shorter than the inner diameter of the volute so that the shaft can be inserted and extracted by sliding it out through the volute.

As regards the turbine seals, preferably one of them is defined by a ring surrounding the shaft and translatable from a recess obtained in the volute so as to move into abutment with a corresponding circular band on the head of the shaft, preferably the main disc, which in this case would extend all the way to the rotor axis so as to ensure a fluid seal, or directly onto the supporting disc. This solution is particularly advantageous for isolating the internal environment of the turbomachine from the external environment during the maintenance procedure.

Drawings

However, further details of the invention will become apparent from the following detailed description with reference to the drawings, in which:

figure 1 is a schematic axially symmetrical cross-sectional view of a first embodiment of a turbomachine according to the invention;

figure 2 is a schematic axially symmetrical cross-sectional view of a second embodiment of a turbomachine according to the invention;

figure 3 is a schematic axially symmetric cross-sectional view of a third embodiment of the turbomachine according to the invention, in a first configuration;

figures 3A and 3B are enlargements of the detail of figure 3 in two different configurations;

figure 4 is a schematic axially symmetric cross-sectional view of a third embodiment of the turbomachine according to the invention, in a second configuration;

figure 5 is a schematic axially symmetric cross-sectional view of a fourth embodiment of the turbomachine according to the invention provided with a first radial centrifugal expansion stage;

figure 6 is a schematic axially symmetrical cross-sectional view of a fifth embodiment of the turbomachine according to the invention;

figure 7 is an enlarged view of a detail of figure 6;

figure 8 is a schematic axially symmetrical cross-sectional view of a sixth embodiment of the turbomachine according to the invention;

figure 9 is a schematic axially symmetric cross-section of a seventh embodiment of the turbomachine according to the invention provided with a first radial centripetal expansion stage;

figure 10 is a schematic axially symmetric cross-sectional view of an eighth embodiment of a turbomachine according to the invention provided with a stepped volute;

figure 11 is a schematic axially symmetrical cross-sectional view of a ninth embodiment of a turbomachine according to the invention, of the bidirectional flow type;

figure 12 is a schematic axially symmetrical cross-sectional view of a tenth embodiment of a turbomachine according to the invention, of the bidirectional flow type;

figure 13 is a schematic section of a first embodiment of a valve for use in a turbomachine according to the invention;

figure 14 is a schematic section of a second embodiment of a valve for use in a turbomachine according to the invention;

figure 15 is a perspective view of the components of the valve shown in figure 14.

Detailed Description

Fig. 1 shows a first embodiment of a turbomachine 1 according to the invention, the turbomachine 1 comprising a shaft 2, a volute 3 for injecting a working fluid to be expanded and discharging the expanded working fluid, and a plurality of expansion stages, in turn defined by an array of stator blades S alternating with an array of rotor blades R.

Looking at fig. 1, the stage furthest to the left is the high voltage stage and the stage furthest to the right is the low voltage stage.

Supporting disks, numbered 10, 20, 30, 40, 50, support the rotor blades.

Bearings

5 and 6 support the shaft 2.

For the purposes of the following description, the volute 3 refers generally to the stationary support component of the turbomachine 1. The volute 3 may in turn be formed of several elements, as will be understood by those skilled in the art.

It should be noted that in the figures, the labyrinth seals are only schematically shown. In fact, in order to constrain the parts to be described, generally having different diameters, it is necessary to provide labyrinth seals, which are in turn defined by surfaces having different diameters.

The stator vanes are fastened to the volute 3 and are therefore stationary; the rotor blades must rotate integrally with the shaft 2. This is achieved by a specific arrangement of the support disks 10-50 which allows to obtain a cantilevered configuration of the turbomachine 1.

Only one of the supporting discs, called main supporting disc 10 for the sake of simplicity, is directly coupled to the shaft 2 (by means of the Hirth-type teeth H in the case shown in the figures), while the remaining supporting discs 20-50 are coupled to the main disc 10 but not directly to the shaft 2, i.e. they do not contact it.

More specifically, as can be seen in the cross-sectional view of fig. 1, the supporting

discs

40, 30 and 20 arranged upstream of the main disc 10 and the disc 50 arranged downstream of the disc 10 are in fact rings with a limited radial extension, that is to say they do not extend all the way to the vicinity of the shaft 2.

A volume or gap 4 is left between the

rings

40, 30, 20, 10 and the shaft 2. The gap 4 is used to house the stator part of the bearing of the seal 5' and the

bearings

5 and 6, thereby allowing the turbine to be designed with the centre of gravity towards the bearings, thus to the left of the main support disk 10, and for inserting the turbine shaft 2 into the

disks

20, 30 and 40 previously assembled in the volute 3 and for allowing the insertion of tools for maintenance.

In practice, each support disc 10-50 has a flanged portion 7 extending axially in a cantilevered manner to effect an abutting coupling with the flanged portion 7 of the adjacent disc. In the example shown in the figures, the flanged portions 7 are bolted to each other by means of bolts 8 so as to form a set of support discs 10-50 rotating integrally with the shaft 2.

As is apparent, the bolts 8 are circumferentially arranged along the flanged portion 7. In the section between two bolts, a flange portion may be obtained in order to lighten the respective disc and to mitigate the effect of the load reduction on the bolts due to the presence of strong tangential tensile stresses with respect to the poisson modulus value of the material, which leads to necking of the disc.

The proposed solution provides the advantage of allowing more expansion stages to be provided upstream of the main support disc 10, so that these stages are supported only by the main disc 10 in a cantilevered manner and not directly by the shaft. The discs 20-40 and 50 are not directly constrained to the shaft 2; instead, the only coupling provided is that with the support disc 10 at the head of the shaft 2, in any case outside the

bearings

5 and 6.

The operation of assembling the turbomachine 1, which can be performed in two ways, is therefore significantly simplified.

According to a first way, the shaft 2 is inserted through the disks 10-50 previously housed in the volute 3, i.e. the shaft 2 can be inserted in the end (from left to right in the figure) together with the

respective bearings

5 and 6.

According to a second way, the shaft 2 and the discs 10-50 are preassembled outside the volute 3 to form an assembly which is then inserted simultaneously (from right to left as seen in the figures) into the volute 3. These elements are then mounted using a method of sliding the mechanical seal and the

bearings

5 and 6 on the shaft itself from the end opposite the main disc 10.

Despite the cantilevered configuration of the stage upstream of the disk 10, the center of gravity of the assembly of rotating elements is still closer to the bearing 6 or even between the

bearings

5 and 6 due to the fact that some portion of the volute 3 can be received in the gap 4 left by the annular shape of the

rotor disks

20, 30 and 40. This is an important feature aimed at reducing the flexibility of the shaft-rotor assembly, thereby allowing to achieve a "stiff" operation of the system, i.e. with a first critical deflection speed high enough to be substantially greater than the rotation speed of the turbine. Obviously, if the designer places multiple discs downstream of the main support disc 10 (to the right of disc 10 in fig. 1), the centre of gravity tends to shift away from the region of the bearings 5, 6 (the moment increases, the system becomes more flexible, the first critical flexure speed decreases). With a given total number of discs of equal respective geometric and mass characteristics, as the number of discs mounted in cantilever fashion towards the system of

bearings

5 and 6 increases, the position of the center of gravity of the rotating mass moves closer to the system of

bearings

5 and 6, thereby causing an increase in the eigenfrequency of the flexure of the rotor/bearing system. The change in the position of the center of gravity also causes the value of the moment of inertia with respect to the center of gravity axis orthogonal to the rotation axis to change. The value of this element affects the eigenfrequency and has to be taken into account according to calculation methods known in the art.

Furthermore, in order to minimize the cantilever mass and thus maximize the value of the first critical deflection speed of the shaft-bearing disk assembly, designers also decide to use lighter materials than ferrous alloys, such as aluminum or titanium, for the blades and/or the bearing disks.

If it is necessary to perform maintenance requiring the disassembly of the mechanical seal, when the turbine is stopped, said sealing ring 9, shown in figure 2, can be operated by translating said sealing ring 9 into abutment with the head of the shaft 2 from the corresponding seat in the volute 3. The temporary seal allows keeping the internal environment of the turbomachine 1 isolated from the external environment during particular maintenance and thus prevents air from entering the turbomachine from the outside or, vice versa, working fluid from leaking to the outside, depending on the pressure inside the stopped turbomachine.

Alternatively, there may be an annular seal that translates over the larger diameter seal, abutting one of the supporting disks of the rotor (preferably the main disk) when in the advanced position. In this case, the shaft 2 can be released from the Hirth tooth without losing the seal. In a further possible configuration, there may be two sealing rings 9, one abutting against the shaft 2 and the other abutting against the main support disc 10, respectively. In this case, the first seal ring is used as a frequently used ring to be used when the turbine is currently stopped, and will preferably be provided with an elastomeric seal gasket, while the second seal ring will be rarely used in the event of unforeseen events requiring disassembly of the shaft 2 and bearing/

housing sleeve assembly

5, 5', 6. Due to the double ring, in particular the elastomer gasket of the innermost seal can be replaced. The shaft 2 can be connected to the main disc with Hirth teeth, as shown in fig. 6 and 7, by means of bolts (depicted using the respective axes of symmetry) or via tie rods 70, to be preferably hydraulically loaded. The tie rods 70 are accessible from the

bearings

5 and 6 sides and each comprise a ring nut 71, an internal hexagonal head 72, a centering cylinder 73 and a threaded body 74 which engages with a corresponding hole of the main support disc 10.

This operation is facilitated by the use of a fastening system, which is fastened by means of the tie rod 11 to be translated, locking the supporting discs 10-50 and preventing them from rotating. The tie rods 11 may be inserted into screw holes 41 formed in the support tray 40. Preferably, each tie rod 11 has its own seal to prevent the working fluid from leaking outside the turbine through the seat of the tie rod 11 itself.

Once inserted in the respective hole 41, the tie rod 11 is fixed on the volute 3 so as to keep the support disc 10-50 locked with respect to the volute 3, allowing the ring 9 to abut against the head of the shaft 2 or the main disc 10, thus obtaining a seal during the maintenance procedure.

Considering again the assembly of the turbomachine 1 and with reference to the embodiment shown in fig. 2, a combination of components as now described may be formed. The pre-assembly is performed outside the volute 3 according to the following sequence:

a. the first stator S on the leftmost side;

b. a rotor R on the support disk 40;

c. a second stator S;

d. the second rotor R on the disc 30 is supported and the

discs

30 and 40 are connected by means of bolts 8 on the opposite flange surface 7;

e. a third stator S;

f. the third rotor R on the disc 20 is supported and the

discs

20 and 30 are connected by means of bolts 8 on the opposite flange surface 7;

g. a fourth stator S;

h. a fourth rotor R on the support disk 10, and by connecting the

disks

10 and 20 by means of bolts 8 on the opposite flange surface 7;

i. a fifth stator S;

j. the fifth rotor R on the disc 50 is supported and if there are larger stages, the

discs

10 and 50 are connected by means of bolts 8 on the opposite flange surface 7, etc.

The stator S is fastened to the portion 31' of the volute 3 by screws or by means of other known techniques, for example by engaging the vanes in special grooves obtained in the volute 3.

The preassembled component combination is then inserted into the volute 3. At this point, the shaft 2 is inserted through the discs 20-50 themselves and along the set path, and then the

bearings

5 and 6 are positioned and held in place by spacers (not shown).

In the main support disc 10, there are one or more through holes 12 to allow pressure equalization between the upstream and downstream portions of the disc 10 itself.

Fig. 3 shows a third embodiment of a turbine 1 which differs from the turbine 1 shown in fig. 2 in that it is provided with a shut-off valve 13 on the flange 7 of the disk 10-50. More specifically, the flanges 7 of the discs 10-50 are perforated, i.e. have a plurality of through holes 14 formed circumferentially thereon. Each through hole 14 is intercepted by a valve 13.

The valve 13 comprises an occlusion element 15 to occlude the respective hole 14; which in the example shown in the figures is a metal ball 15. The spring 16 pushes the blocking element 15 away from the hole 14 in order to open the passage. When the discs 10-50 rotate, the spring force of the spring 16 is counteracted by the centrifugal force exerted on the balls 15. The pretension of the spring 16 is particularly selected such that the aperture 14 remains closed when the turbine 1 is operating at a speed above a certain intermediate speed.

Instead, the shut-off valve 13 automatically opens the hole 14 when the turbine rotates at a speed lower than said intermediate speed, to allow the discharge of the working fluid in the liquid phase, which may remain in the gap 4, or of the lubricating oil, which may leak from the rotating seals of the turbine.

In particular, in fig. 3 and 3B, the turbine is stopped and the valve 13 is opened (the tie rod 11 engages in the disc 40 and locks it). In fig. 3A and 4, the valve 13 is closed (the turbine is rotating at a higher than intermediate speed or at nominal speed).

Fig. 4 shows the same turbine as fig. 3, but with the valve 13 closed.

Fig. 5 shows a fourth embodiment of the turbine 1, which differs from the previous turbines in that the first expansion stage is of the centrifugal radial type and the second stage comprises an array of angular stator blades, which are branched off in the axial direction. The remaining stages are axial flow as in the previously described embodiment.

In particular, by adding at least one radial stator blade assembly, a system for varying or intercepting flow, such as a variable pitch blade system, may be provided, thereby reducing costs relative to an axial stator blade system.

Fig. 6 shows an embodiment with a solid shaft 2. The shaft 2 is coupled to the main support disc 10 by means of Hirth teeth and a plurality of tie rods 70, shown enlarged in fig. 7. The turbine comprises a sealing ring 9' translated from the volute 3 and having a larger diameter than the ring 9 shown in figure 2. The ring 9' moves against the main support disc 10 in order to obtain a seal.

Although not shown in the figures, in one embodiment of the turbomachine there may be two translational seals 9 and 9' used alternately or jointly for maintenance.

Fig. 8 shows an embodiment with a hollow shaft 2. The tie rod 2' is arranged therein and screwed to the main support disk 10. It is an alternative to locking the Hirth teeth.

Fig. 9 shows yet another embodiment in which the first expansion stage is centripetal radial. In this case, the corner blades are rotor blades supported by the disk 40.

Figure 10 shows a further embodiment in which the volute 3 comprises a grooved (i.e. stepped) inner ring 31. The arrays of stator vanes S are individually fastened to the respective coupling rings 32-35 to couple with the grooved inner ring 31.

In practice, the coupling rings 32-35 can be screwed onto the grooved inner ring 31 one after the other in succession at one step. This screwing is performed outside the turbomachine and, finally, the ring 31 with the stator array S, the supporting discs 10-50 and the rotor R are inserted in the volute 3 and fastened thereto.

The preassembled combination consisting of the ring 31 with the stator array S, the support discs 10-50 and the rotor array R can simply be screwed onto the volute 3.

Fig. 11 shows a further embodiment of the turbomachine 1, characterised by being of the bidirectional flow type. The working fluid inlet is preferably located at the median plane of the main support tray 10. Reference numeral 36 denotes a ring to be coupled with the inner ring 31 of the scroll casing 3. The ring 31 is fastened from right to left and then bolted to the volute 3. The coupling ring 36 includes two symmetrically split stator arrays S that split the flow of working fluid on opposite sides. The remaining stator S and rotor R arrays alternate in a mirror-symmetrical manner with respect to the main support disc 10. A passage P is provided between the ring 36 and the

support discs

10 and 20 to prevent pressure imbalance. This allows the center of gravity of the rotor portion of the turbine to be located just above the main support disk 10.

Fig. 12 shows a tenth embodiment of a turbomachine which is similar to the previous embodiment, but differs in that two mirror rotor arrays R, axially branched, are provided on opposite sides, after the first stator array S, into which the working fluid enters. These rotor arrays R are each supported by a main support disc 10.

The assembly views of the turbine shown in fig. 11 and 12 are similar to those described for the other embodiments.

Fig. 14 to 15 show one possible configuration of the shut-off valve 13 provided with a body 131 on which the blocking element 15 is mounted, for example a cylinder with a spherical end that can slide radially on a bearing pin 133 and is resisted by a spring 16. The obturating element 15 can be radially moved to intercept or uncover the hole 14 obtained in the flanged portion 7 of the respective supporting disk 10-50. The body 131 has a threaded portion 132 to be screwed into the bore 14.

A further embodiment of the shut-off valve 13 is shown in fig. 13. Inside a set of blades 135 held together by riveting pins 136 or screws, there are mounted occlusion balls 15. The ball 15 is free to translate, with play inside the space formed by the set of blades 135, thus being able to engage when centrifugal force pushes it against the hole 14. The blade 137 elastically supports the blade assembly 135 and the ball 15. The vanes 138 act as spacers. The pin 139 has the function of centering the fastening screw 140 in the corresponding hole 142 (for the pin) and hole 141 for the screw 140.

Fig. 13 shows the valve not mounted on the corresponding disc. The leaf springs 137 and spacers 138 hold the balls 15 away from the bore 14 when the turbine is rotating at a lower speed relative to the intermediate speed (defined above). At higher speeds, the leaf spring 137 flexes and the occlusion ball 15 comes into abutment with the aperture 14, thereby occluding the aperture 14. The designer can modify the elasticity of the

springs

137 and 16 and the mass of the movable system in order to determine the intermediate speed value at which the valve itself operates.

Claims

1. A turbine (1) designed to operate in an Organic Rankine Cycle (ORC) or kalina cycle or a steam cycle, comprising a shaft (2) supported by at least two bearings (5, 6), a plurality of arrays of rotor blades (R) and corresponding supporting discs (10-50) and a plurality of arrays of stator blades (S), wherein one of said supporting discs (10-50), called main supporting disc (10), is directly coupled with said shaft (2) in an outboard position with respect to said bearings (5, 6) and the remaining supporting discs (20-50) are constrained on said main supporting disc and are constrained one after the other, but not directly on said shaft (2),

characterized in that at least some of the remaining support disks (20-40) are constrained on the main support disk (10) by extending in cantilever fashion from the same part of the bearing (5, 6) that supports the shaft (2), so that the centre of gravity of the rotor part of the turbine (1) is displaced more towards the bearing (5, 6), or at least coincides therewith, with respect to the position of the centre of gravity of one of the main support disks (10).

2. Turbine (1) according to claim 1, wherein at least some of the remaining support disks are constrained on the main support disk (10) by extending in a cantilevered manner in a direction opposite to the bearings (5, 6) supporting the shaft (2), so that the number of turbine stages increases.

3. Turbine (1) according to claim 1 or 2, wherein the remaining support discs (20-50) except the main support disc (10) are provided with a central hole, i.e. they are rings, such that a gap (4) is defined between each ring and the shaft (2) and extends as required to receive stator components.

4. Turbine (1) according to claim 1 or 2, wherein the main support disc (10) and the remaining support discs (20-50) are bolted to each other and the main support disc (10) is constrained on the shaft to fit in a pressurized oil condition by means of a coupling selected from: flange, bolt, face tooth (H), conical coupling, keyed profile, one or more barrel couplings.

5. Turbine (1) according to claim 1 or 2, wherein the array of rotor blades (R) located furthest away from the main support disc (10) on the bearing (5, 6) side is a high pressure rotor blade.

6. Turbine (1) according to claim 1 or 2, wherein the main support disc (10) and the series or combination of the remaining support discs (20-50) can be preassembled outside the turbine (1) for simultaneous installation in the turbine.

7. Turbomachine (1) according to claim 1 or 2, comprising a stator portion on which the array of stator blades (S) is constrained in an alternating manner with the array of rotor blades (R), wherein the stator portion defines a rotary body (31) provided with a stepped inner surface and each array of stator blades (S) is fastened on at least one of said steps by means of a ring (32-35), and in this case also the main bearing disk (10) and the remaining bearing disks (20-50) can be inserted one by one into the stator portion.

8. Turbine (1) according to claim 1 or 2, wherein the main support disc (10) and each of the remaining support discs (20-50) comprises at least one flanged portion (7) projecting in cantilever fashion towards the flanged portion (7) of the adjacent support disc for abutment coupling, and comprises one or more through holes (14) passing through the flanged portion (7) and a shut-off valve (13) of each through hole (14), configured for:

-closing the through hole (14) during operation of the turbine (1) and thus avoiding the passage of a working fluid,

-opening the through hole (14) when the turbine (1) is slowly rotating or stopped, so as to allow the discharge of the working fluid in liquid phase, accumulated in the volume near the flanged portion (7), or of the lubricating oil leaking through the seals of the turbine (1).

9. Turbomachine (1) according to claim 8, wherein each shut-off valve (13) comprises:

-a blocking member (15) for blocking the through hole (14) obtained in the flanged portion (7) of the respective supporting disk, and

-a biasing elastic member (16) designed to push the blocking member (15) in the position of the open through hole (14), and

wherein the biasing force of the biasing spring (16) is such that the centrifugal force exerted on the closing element (15) is higher than the biasing force of the biasing spring during operation of the turbine, such that the through-opening (14) remains closed when the turbine (1) is operating at nominal speed and opens when the turbine (1) is stopped or operating at low speed.

10. Turbomachine (1) according to claim 8, wherein each shut-off valve (13) comprises:

-a spherical closing member (15);

-a housing for the obturating member (15), which is partially open towards the through hole (14) so that at least a portion of the obturating member (15) can protrude from the housing itself towards the through hole (14);

-an elastic support member (137) for supporting the housing,

wherein the housing is constrained to the elastic support member (137) and

wherein, after the bending of the elastic support member (137), the blocking member (15) intercepts the through hole (14) or moves away from the through hole so that the through hole remains open.

11. Turbine (1) according to claim 1 or 2, wherein one or more passages (12) for balancing the pressure upstream and downstream of the same main support disc (10) are obtained through said main support disc (10).

12. Turbomachine (1) according to claim 1 or 2, wherein the first expansion stage is centripetal radial or centrifugal radial in the expansion direction of the working fluid.

13. Turbine (1) according to claim 1 or 2, comprising at least three support disks upstream of the main support disk (10) and one or more support disks downstream of the main support disk, and a respective expansion stage of the working fluid.

14. Turbine (1) according to claim 1 or 2, wherein the turbine comprises a volute (3) and the head of the shaft has a diameter smaller than the inner diameter of the volute, so that the shaft can be extracted by sliding it out through the volute (3).

15. Turbomachine (1) according to claim 8, comprising at least one seal (9, 9') defined by a ring surrounding the shaft (2) and translatable from a recess obtained in a volute (3) or other stationary component, so as to move into abutment with a respective circular seat obtained on the end of the shaft, designed to couple with the main support disc (10), or against one of the main support disc (10) and the remaining support discs (20-50).

16. Turbine (1) according to claim 1, of the bidirectional flow type, comprising a plurality of expansion stages located on both sides of one of the main and the remaining support discs (10, 20-50), and wherein the working fluid starts expanding at such a support disc via a radial inlet and is axially split into two flows at opposite portions of said one support disc.

17. Turbine (1) according to claim 16, wherein the fluid starts expanding at the main support disc (10) through a radial inlet and is split axially into two flows at opposite parts of the main support disc (10).

18. Turbine (1) according to claim 16 or claim 17, comprising an annular chamber (P) in fluid communication between the outlet of the first stator upstream of said one supporting disc, in which the fluid starts to expand, and the outlet of the first stator downstream of said one supporting disc itself.

19. Turbine (1) according to claim 16 or claim 17, wherein the first expansion stage for the passage of the fluid is of centripetal radial type, with a bidirectional flow rotor connected to said one supporting disk.

20. Turbomachine (1) according to claim 3, wherein the gap extends as required to house the seals and bearings (5, 6) and the respective housing sleeve (5') and the central portion of the volute (3).

21. Turbomachine (1) according to claim 4, wherein the bolts are stud bolts.

22. Turbomachine (1) according to claim 4, wherein the keyed profile is a splined profile.

23. Turbomachine (1) according to claim 7, wherein the stator part is a volute (3).

24. The turbomachine (1) of claim 10, wherein the housing comprises a set of blades (135) defining an internal cavity.

25. Turbomachine (1) according to claim 10, wherein the elastic support members (137) are elastic plates in turn fastened to the respective support disc in the vicinity of the through holes (14).

26. Turbine (1) according to claim 15, wherein the through hole is located on a larger diameter than the seal.

27. Turbine (1) according to claim 15, wherein said circular seat is designed to rest against said main support disc (10).

28. An ORC rankine cycle plant comprising a turbine (1) according to any one of claims 1-27.

29. Kalina cycle plant comprising a turbine (1) according to any one of claims 1 to 27.

30. A water vapor cycle apparatus comprising a turbine (1) according to any one of claims 1-27.